RETROREFLECTORS FOR REMOTE DETECTION
A detection system includes a retroreflector and a layer of material over the retroreflector, the material being subject to change in transmission with respect to an optical property of radiation, e.g. wavelength or polarization, with exposure to a phenomenon. The retroreflector and layer are illuminated from a radiation source of multiple aspects of the optical property. A sensor senses radiation retroreflected back through the layer. The retroreflector may, for example, be an array of or individual prisms or an array of or individual cat's eye microspheres. The layer of material above the retroreflector can include a colorimetric dye. In an embodiment, the retroreflector and layer are on the surface of a carrier that moves through a medium, e.g. a projectile or vehicle moving through the air. In a method of detecting a phenomenon, retroreflective elements are distributed in an array, as in the atmosphere or across a region of ground.
This application claims the benefit of U.S. Provisional Application No. 61/414,810, filed on Nov. 17, 2010.
The entire teachings of the above application are incorporated herein by reference.
GOVERNMENT SUPPORTThis invention was made with government support under Grant No. FA8721-05-C-0002 awarded by the U.S. Air Force. The government has certain rights in this invention.
BACKGROUND OF THE INVENTIONColorimetric dyes are among the oldest chemical detection technologies, in use for at least 350 years and perhaps even since antiquity. See A. A. Baker, A History of Indicators, Chymia 9 (1964) 147-167. Sensors based on colorimetric detection are commercially available for a wide range of compounds and conditions. Because of their simple visual readout, detection systems based on colorimetric indicators can be very inexpensive and are thus widely deployed. For example, M8 and M9 colorimetric papers remain, over 45 years after their initial deployment, the most widely deployed detectors of chemical warfare agents (CWA) in the United States Military. See J. K. Smart, History of Chemical and Biological Detectors, Alarms, and Warning Systems, United States Army Soldier and Biological Chemical Command, Aberdeen, Md., 2000; Field Manual 3-3 Chemical and Biological Contamination Avoidance, United States Army, 1992.
The readout of colorimetric sensors is typically done by an operator in close proximity to the sensor who measures the color change by eye. In the case of detectors for hazardous materials, this presents difficulty for the operator who must physically enter the hazard zone. This requires personnel with special training, cumbersome personal protective equipment, and provision for decontamination upon return from the hazard zone. All of these preparations add up to turn an inexpensive and rapid sensor into a time consuming and expensive sensing system. Even if hazardous materials are not involved, reading out a large number of colorimetric sensors, for example to map the extent of contamination, is time consuming as the operator must physically approach each one. Proximity readout also presents problems for sensors in remote locations, for example monitoring water quality in remote lakes, where the difficulty of access renders visiting the sensors for readout impractical.
Discrete retroreflectors (i.e. not retroreflective tapes) have been used as part of a spectrometer for remote sensing of atmospheric vapors, transforming an otherwise bistatic measurement of the atmosphere into a monostatic one. See Z. Bacsik, J. Mink, and G. Keresztury, FTIR spectroscopy of the atmosphere. I. Principles and methods, Appl. Spectrosc. Rev. 39 (2004) 295-363. A sensor that uses optical changes in the path to a retroreflector is described in U.S. Pat. No. 6,668,104 to Mueller-Fiedler et al. A chemical sensor for remote interrogation having a surface relief structure, e.g., a surface grating, positioned over a retroreflector is disclosed in U.S. Pat. No. 7,262,856 to Hobbs et al. U.S. Pat. No. 5,822,074 to V. A. Deason et al. describes using a retroreflector that is partially isolated from the environment for remote readout of colorimetric detectors. There, a user must know where the isolated portion lies in order to compare that portion with the exposed portion. Unfortunately, this limits such a device to uses where the orientation of the retroreflector is known.
SUMMARY OF THE INVENTIONA detector for detecting exposure to any of a number of phenomena includes a retroreflector and a layer of material over the retroreflector, the material being subject to change in transmission with respect to an optical property of radiation with exposure to a phenomenon. The retroreflector and layer are illuminated from a radiation source of multiple aspects of the optical property, and a sensor senses radiation retroreflected back through the layer.
The sensor may be wavelength dependent. The retroreflector may, for example, include a prism or a cat's eye microsphere or an array of retroreflective elements, such as an array prisms or an array of cat's eye microspheres. In an embodiment, the material is subject to color change with exposure to the phenomenon and the radiation source is a source of radiation at multiple wavelengths. For remote detection, the light source preferably comprises at least two lasers of different wavelengths. For less remote detection, a non-collimated radiation source, even a flashlight of white light, may be used.
The radiation source and the detected wavelengths may be visible or non-visible. Sensors of more than two wavelengths may be used. For example, the sensor can include plural filters for different wavelengths. The layer above the retroreflector can include a colorimetric dye, for example an azobenzene dye that bleaches in the presence of organophosphates but does not bleach in the presence of common interferents.
The material may also be subject to change in polarization, optical chirality, or non-linear properties (e.g., variation in transmission with light intensity) with exposure to the phenomenon. In an embodiment, the material is subject to change in polarization and the radiation source is a source of radiation at multiple polarizations.
In some embodiments, the retroreflector and layer are on the surface of a carrier that moves through a medium or a region, such as a projectile, a ground vehicle, an airplane, an unmanned air vehicle (UAV), an unmanned ground vehicle (UGV), a submarine, or a person.
In a novel method of using the detector, detector elements are distributed in an array, as in the atmosphere or across a region of ground. The level of the detected phenomenon can then be mapped across the array. The retroreflective elements may be projectiles or attached to projectiles or other carriers and the response may be sampled as the projectiles or carriers move through the atmosphere or across the ground.
A method of detecting a phenomenon includes illuminating a retroreflector with radiation at multiple aspects of an optical property of the radiation through a layer of material over the retroreflector, the material being subject to change in transmission with respect to the optical property with exposure to the phenomenon. The method also includes sensing radiation retroreflected from the retroreflector.
The retroreflector, which can include a cat's eye microsphere or an array of prisms, may be illuminated with radiation at multiple wavelengths, e.g.,with multiple lasers, and the material may be subject to color change. In an embodiment, the retroreflector is illuminated with white light and sensing radiation includes filtering at different retroreflected wavelengths. The retroreflector may be illuminated with radiation at different aspects of the optical property at different times.
The phenomenon to be sensed or detected by the devices and method described herein can include any combination of temperature, pH, and the presence or absence of a chemical.
A detection system includes an array of retroreflective elements distributed over a region, each retroreflective element having a change in optical characteristics with exposure to a phenomenon. Also included are a radiation source to illuminate the retroreflective elements and a sensor sensing radiation reflected from the retroreflective elements.
The change in optical characteristics can be any change in an optical property which affects transmission selectively, such as a change in color or change in polarization. The retroreflective elements may be projectiles or attached to carriers and may be distributed through the atmosphere or across a region of ground. Each of the distributed retroreflective elements can include one or more prisms or one or more cat's eye microspheres. The radiation source can include plural lasers of different wavelengths. Alternatively or in addition, the sensor can include plural filters for different wavelengths. In an embodiment, the retroreflective elements have a varied response in retroreflected wavelength with exposure to the phenomenon.
A method of detecting a phenomenon includes distributing an array of retroreflective elements over a region, each retroreflective element having a change in optical characteristics with exposure to the phenomenon; illuminating the array of retroreflective elements with radiation; and sensing radiation retroreflected from the retroreflective elements.
The retroreflective elements may be illuminated with white light and sensing radiation can include filtering at different retroreflected wavelengths. Alternatively or in addition, the retroreflective elements are illuminated with different wavelengths at different times. For example, lasers may be used to illuminate the array of retroreflective elements.
In one embodiment, a cat's eye retroreflector is coated with a layer of material that changes transmission with respect to an optical property of radiation when exposed to a phenomenon to be sensed.
The cat's eye retroreflector may be a projectile and may be a microsphere. The material can include a material that changes color with exposure to the phenomenon, such as a colorimetric dye.
A detection device includes a retroreflector and a layer of material over the retroreflector, the material being subject to change in transmission with respect to an optical property of radiation with exposure to a phenomenon.
Further, the detection device can include a radiation source of multiple aspects of the optical property to illuminate the retroreflector through the layer and a sensor sensing radiation reflected through the layer.
Although a wavelength dependent retroreflective element is preferred in this application, other technologies, such as presented in U.S. Pat. No. 5,822,074 (incorporated by reference in its entirety), may be used in the individual retroreflective elements of the array.
Detection systems and methods using wavelength dependent retroreflective elements according to embodiments of the invention offer advantages over other technologies. For example, in the '074 patent, differential readings are determined by exposing one region to the detected environment while protecting another; whereas, in the system disclosed here, differential readings are based on wavelength in viewing a single region. The present approach is suitable for detecting limited size drops, such as those from a pesticide that has been sprayed or any other aerosol. In contrast, devices that depend on differential readings from two regions of a retroreflector may not work because the droplets may not cover both regions. With the present wavelength dependent approach, measurements can be made independent of non-measured phenomenon such as dirt which affect both wavelengths the same, while dirt on only one region of the '074 patent device will affect the regions differently and thus affect the output. Further, it would be difficult to isolate the two regions of the '074 patent for phenomena such as temperature.
Another advantage of the present approach is that the orientation of the retroreflective device need not be known to detect exposure to a phenomenon, for example where the retroreflective device is not attached to a fixed support or where one or more retroreflective devices are thrown or dropped into the region to be measured.
Further, unlike colorimetric surface structures, such as surface gratings, which reflect incident light in different directions to change color, the colorimetric layer or colorimetric dye described herein changes color by changing absorption of incident light. Advantageously, the colorimetric dye can be specific to a phenomenon to be measured, e.g., exhibiting a color change specific to the presence of organophosphates.
The ability to detect remotely presents significant advantages over currently available capabilities. As just one example, current US Air Force procedure for suspected chemical attacks is to deploy a grid of colorimetric M8 paper targets over the vulnerable area. After the attack, these targets must be read by airmen at relatively close range, tens of meters at most, subjecting them to contamination by the very chemicals they are attempting to detect. With the present approach, a retroreflective sensor can be read from a kilometer or more, or from an aircraft, well outside the range of potential contamination. In addition, the low cost of the sensor elements, and the modest cost of the illuminator/receiver, allows the dense deployment of sensors in applications which would not otherwise be economically feasible. With the present approach, retroreflective sensors can be deployed in large numbers to densely cover areas. In addition, such sensors may be used for remotely detecting low vapor pressure surface contaminants, a significant area of interest to the military.
Embodiments according to the present approach can be used to remotely monitor temperature. For example, a remote readout thermometer can include a retroreflector coated with a liquid crystal material that changes its polarization state in response to temperature.
Retroreflective elements and surfaces as described herein may also be used in standoff spectroscopy. On the retroreflectors' well defined and highly reflective surfaces, spectra measured in reflection may correlate with the large available library of absorbance spectra, allowing remote identification of unknowns on their surfaces.
A retroreflective detection system according to the present approach is described in a paper by Michael Switkes et al., “Retroreflectors for remote readout of colorimeteric sensors”, Sensors and Actuators B, 160: 1244-1249 (2011), which is incorporated by reference in its entirety.
The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention.
A description of example embodiments of the invention follows.
In an embodiment, device 100 includes a retroreflector, including a textured layer 101 and a clear protective overcoat 103, which is coated with a colorimetric layer 104 that includes a dye 106. In its native state 107, dye 106 absorbs one wavelength of light 110 and allows another wavelength of light 112 to pass. Dye 106, however, allows both wavelengths to pass when activated 108 by a phenomenon to be sensed, for example, when the dye is exposed to a chemical agent or to a change in temperature. Thus, when dye 106 is activated, retroreflector 102 reflects both wavelengths through colorimetric layer 104. Suitable dyes for dye 106 are described below.
The combination of colorimetric indicators with retroreflective substrates transforms what has been a proximity measurement using standard colorimetric sensors, into a measurement that can be performed at a distance. As their name indicates, retroreflective materials return light toward its source with high efficiency over a broad range of angles of incidence; unlike a mirror, there is no need for careful alignment of a retroreflector. Because retroreflectors are designed to reflect the light incident on them in the direction of the source rather than scattering or reflecting it away, their use increases the range at which optical changes can be detected. Retroreflective materials are commercially available and ubiquitous in road marking, vehicle conspicuity, and personnel visibility applications, among others. They are also remarkably inexpensive. Thus, deployment of large numbers of unpowered sensing elements is possible, opening up applications not feasible with expensive sensors.
Because the retroreflective material is highly efficient, even low-powered illumination allows readout at long distances. Using a simple model, one can predict the performance. The signal, i.e. number of photons returned to a single pixel of the receiver by the retroreflector Nr is
Ni is the number of photons emitted from the illuminating laser, Ai the total area illuminated by the laser, Apixel the area of retroreflector imaged by a single detector pixel, Ω the solid angle of imaging aperture, RA the coefficient of retroreflection, φ the fraction of the pixel area which has changed color, and T0 and T1 the round-trip transmission in the unchanged and changed states of the colorimetric film, respectively. The aperture r of the imaging optic determines the solid angle; for ranges R>>r, Ω≈πr2/R2.
The coefficient of retroreflection RA is a measure of the efficiency of the retroreflector material. It is typically quoted by manufacturers in cd lux−1 M−2 which is dimensionally equivalent to sr−1; typical values of RA for commercially available retroreflectors are in the range of 500-1000 sr−1 whereas a perfectly diffuse reflector would have RA=½πr=0.16 sr−1. To confirm this performance, the return from a sample of commercially available retroreflector material (P-82, Reflexite Inc., New Britain, Conn.) at 660 nm was measured, along with the return of a mirror and a diffuse reflector (white Tyvek, DuPont, Wilmington, Del.).
To detect changes in the dye color remotely while excluding other causes of changing light intensity, for example dirt on the surface of the retroreflector, the return at two wavelengths, and thus different values of T0 and/or T1, is compared. The ratio of photons returned at these two wavelengths, Nrλ
Since CWA, the primary target analytes, are generally encountered in small, concentrated droplets, the analysis here assumes a significant color change, T0/T1≈10 over a small area on the surface of the sensor. In this case, the limit on the expected performance of a retroreflective detection system is the ability to detect sub-pixel (φ<1) changes in the dye layer. In other cases, particularly with dilute analytes, the limit could be the ability to distinguish the color change itself.
At 1 km, a 10 cm telescope has diffraction-limited resolution of ˜5 mm. As an example, HPAC was used to calculate the distribution of expected droplet sizes for a chemical attack with a thickened VX -filled SCUD missile. See HPAC Hazard Prediction and Assessment Capability, Defense Threat Reduction Agency, Fort Belvoir, Va. 1999. The median drop diameter is ˜1 mm, but near the edges of the contaminated area, where mapping might be most useful, droplets are significantly smaller, with an average of <0.5 mm. Malathion droplets sprayed in pest control efforts are smaller still with a mean size of ˜275 μm. See T. Younglove, and P. M. McCool, Droplet size characterization of three aerial malathion spray programs, Bull. Environ. Contam. Toxicol. 53 (1994) 493-500. However, HPAC calculates the droplet size in air, whereas the colorimetric dye relies on interaction with a droplet on its surface. Therefore, φ depends on the size of color change on the surface of the retroreflector itself, and thus on the contact angle θc between the droplet and the retroreflector surface. The contaminated area φ can thus be increased by engineering a reduction in contact angle, causing the droplet to spread as much as possible on the retroreflector surface.
To quantify this, one can calculate the expected performance of a remote colorimetric retroreflector with a diffraction-limited imaging system. Assuming a 10 cm telescope and a commercially available scientific camera (EM11000, Princeton Instruments, Trenton, N.J.) with dark noise of 4000 e−/s, and a colorimetric dye with an on/off ratio T1/T0=10 at λ1, fixing a false alarm rate of 1 in 2×106 gives a detection threshold of Nrλ
Components of an embodiment of a retroreflective sensing system for the remote detection of organophosphate pesticides or nerve agents are described herein. In addition to a commercially available retroreflective tape (P-82, Reflexite, New Britain, Conn.), the exemplary sensor system includes a colorimetric dye, such as one of the custom synthesized colorimetric dyes described below, a polymer system for coating the dye onto the retroreflector, and an optical detection system for illuminating the retroreflectors and detecting the color change remotely.
Azobenzene DyesA set of colorimetric dyes that bleach in the presence of organophosphates but not in the presence of many common interferents were synthesized. This class of colorimetric dyes is based on a 2-(2-(dimethylamino)phenyl)ethanol structure that acts as a donor in a charge-transfer azo dye with a sufficiently electron-poor acceptor group. The first dye that was investigated was prepared by the method of Costero and co-workers who also investigated these materials for the colorimetric detection of nerve agent simulants. See A. M. Costero, S. Gil, M. Parra, P. M. Mancini, R. Martinez-Máñez, F. Sancenón, and S. Royo, Chromogenic detection of nerve agent mimics, Chem. Comm. (2008) 6002-4; A. M. Costero, M. Parra, S. Gil, R. Gotor, P. M. E. Mancini, R. Martinez-Manez, et al., Chromo-Fluorogenic Detection of Nerve-Agent Mimics Using Triggered Cyclization Reactions in Push-Pull Dyes, Chem.-Asian J. 5 (2010) 1573-1585. The effect of the electron-poor acceptor was also investigated by changing the substitution on that group. The synthesis of these dyes is shown in
For coating on the retroreflective surface, the dye can be mixed with a polymer.
This polymer is an important component of the sensing system and prefereably, should meet a number of criteria. First, it should provide an even, optically transparent coating on the retroreflector's protective top layer. It should also be durable in the sensing environment over the time required for a particular sensing application. In addition, the polymer itself should not react with the target chemical or likely contaminants. Finally, it should be permeable to the analyte to allow it to reach and react with the dye rapidly. As detailed above, the polymer can further enhance the sensing system by promoting the spreading of the target analyte, turning a small volume of contaminant into a large area of color change on the surface of the sensor.
Embodiments of the invention use a polyester, poly(1,4-butylene adipate), which fulfills many of these criteria. As seen in
A component of the sensing system is the illuminator/receiver, an example of which is illustrated in
Preferably, the reflected light will be measured at two or more wavelengths whose reflectivity is affected differently by the color change allowing other causes of reflectivity change (e.g. dust on the substrate) to be excluded. In the illuminator/receiver system shown in
The prototype illuminator/receiver system 900 described above can, for example, detect a 1 μl droplet of malathion on a retroreflective target at the a distance of 150 m, outdoors in sunlight.
With the present approach, wavelength selection may be accomplished at the radiation source or at the sensor, or both, which can mitigate the effect of stray light from the environment. In one possible mode, the retroreflector is illuminated with white light and a wavelength dependent sensor is used to sense the reflected light. The wavelength dependent sensor may use filters to sense reflected light at selected wavelengths. In another possible mode, the retroreflective element is illuminated using one or more specific wavelength light sources, e.g., two lasers as shown in
As shown in
Described herein are a new indicator dye specific to organophosphate contaminants and an inexpensive retroreflector-based system to read out that dye remotely. Performance modeling indicates that such a system can be used at kilometer ranges for small droplets of contamination. Such a system may be used for hazardous chemical detection at fixed sites. For example, the United States Air Force currently relies on a colorimetric paper placed on a grid of stands to detect and map the extent of a suspected chemical attack on an airbase. See Air Force Manual 10-2602 Nuclear, Biological, Chemical, and Conventional (NBCC) Defense Operations and Standards Review, United States Air Force, 2003. Reading out such a system post attack requires trained personnel to visit each stand with the attendant risks and requirements for personal protective equipment and provisions for decontamination. It is also slow. In contrast, a retroreflector-based system with the same grid layout can eliminate the risk to personnel, and measure the same contamination in a fraction of the time.
As in conventional hazardous chemical detection, applications of pesticides is often monitored with cards whose readout, while not posing the same risks, is still time consuming and thus expensive. Pre-positioned retroreflectors, such as those shown in
Retroreflectors according to embodiments of the invention may also be useful in mapping contamination which has already occurred. As illustrated in
The retroreflective elements 1302 of
Embodiments for retroreflector-based remote sensing may use specific indicator dyes developed or adapted for each sensing target. For droplet sensing applications, maximum analyte spreading is desirable, so an appropriate polymer system or other means of promoting analyte spreading may be used. For many applications, weather resistance is desirable, and the dyes and polymers may be selected for their environmental stability. For kilometer range performance beyond the 150 m demonstrated in
The retroreflective sensors described herein need not be limited to hazardous chemical detection. For example, a retroreflector with a pH or temperature sensitive layer attached to a buoy could be used to monitor the condition of a body of water. Because of their retroreflective nature, sensors spread out over many kilometers could be monitored from a single station (see
The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety.
While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
Claims
1. A detection system comprising:
- a retroreflector;
- a layer of material over the retroreflector, the material being subject to change in transmission with respect to an optical property of radiation with exposure to a phenomenon;
- a radiation source of multiple aspects of the optical property to illuminate the retroreflector through the layer; and
- a sensor sensing radiation reflected through the layer.
2. A detection system as claimed in claim 1 wherein the retroreflector comprises a prism.
3. A detection system as claimed in claim 1 wherein the retroreflector comprises a cat's eye microsphere.
4. A detection system as claimed in claim 1 wherein the retroreflector comprises an array of retroreflective elements.
5. A detection system as claimed in claim 1 wherein the material is subject to color change with exposure to the phenomenon and the radiation source is a source of radiation at multiple wavelengths.
6. A detection system as claimed in claim 5 wherein the radiation source comprises plural lasers of different wavelengths.
7. A detection system as claimed in claim 5 wherein the sensor comprises plural filters for different wavelengths.
8. A detection system as claimed in claim 5 wherein the material comprises a colorimetric dye.
9. A detection system as claimed in claim 1 wherein the material is subject to change in polarization with exposure to the phenomenon and the radiation source is a source of radiation at multiple polarizations.
10. A detection system as claimed in claim 1 wherein the retroreflector and layer are on the surface of a carrier that moves through a medium.
11. A method of detecting a phenomenon comprising:
- illuminating a retroreflector with radiation at multiple aspects of an optical property of the radiation through a layer of material over the retroreflector, the material being subject to change in transmission with respect to the optical property with exposure to the phenomenon; and
- sensing radiation retroreflected from the retroreflector.
12. The method of claim 11 wherein the retroreflector is illuminated with radiation at multiple wavelengths and the material is subject to color change with exposure to the phenomenon.
13. The method of claim 12 wherein the retroreflector is illuminated with lasers.
14. The method of claim 12 wherein the retroreflector is illuminated with white light and wherein sensing radiation comprises filtering at different retroreflected wavelengths.
15. The method of claim 11 wherein the retroreflector is illuminated with radiation at different aspects of the optical property at different times.
16. The method of claim 11 wherein the retroreflector is illuminated with radiation at different polarizations and the material is subject to change in polarization with exposure to the phenomenon.
17. The method of claim 11 wherein the phenomenon includes any combination of temperature, pH, and the presence or absence of a chemical.
18. A detection system comprising:
- an array of retroreflective elements distributed over a region, each retroreflective element having a change in optical characteristics with exposure to a phenomenon;
- a radiation source to illuminate the retroreflective elements; and
- a sensor sensing radiation reflected from the retroreflective elements.
19. The detection system of claim 18 wherein the retroreflective elements are distributed through the atmosphere.
20. The detection system of claim 18 wherein the retroreflective elements are distributed across a region of ground.
21. The detection system of claim 18 wherein each retroreflective element comprises a prism.
22. The detection system of claim 18 wherein each retroreflective element comprises a cat's eye microsphere.
23. The detection system of claim 18 wherein the retroreflective elements have a varied response in retroreflected wavelength with exposure to the phenomenon.
24. A method of detecting a phenomenon comprising:
- distributing an array of retroreflective elements over a region, each retroreflective element having a change in optical characteristics with exposure to the phenomenon;
- illuminating the array of retroreflective elements with radiation; and
- sensing radiation retroreflected from the retroreflective elements.
25. The method of claim 24 wherein the retroreflective elements are illuminated with multiple wavelengths and wherein sensing radiation comprises filtering at different retroreflected wavelengths.
26. The method of claim 24 wherein the retroreflective elements are illuminated with different wavelengths at different times.
27. A cat's eye retroreflector coated with a layer of material that changes transmission with respect to an optical property of radiation when exposed to a phenomenon to be sensed.
28. The retroreflector of claim 27 wherein the retroreflector is a microsphere.
29. The retroreflector of claim 27 wherein the material comprises a colorimetric dye.
30. A detection device comprising:
- a retroreflector; and
- a layer of material over the retroreflector, the material being subject to change in transmission with respect to an optical property of radiation with exposure to a phenomenon.
31. The detection device of claim 30 wherein the retroreflector and layer are on the surface of a carrier that moves through a medium.
32. The detection device of claim 30 wherein the retroreflector comprises a prism.
33. The detection device of claim 30 wherein the retroreflector comprises a cat's eye microsphere.
34. The detection device of claim 30 wherein the phenomenon includes any combination of temperature, pH, and the presence or absence of a chemical.
35. The detection device of claim 30 further comprising a radiation source of multiple aspects of the optical property to illuminate the retroreflector through the layer and a sensor sensing radiation reflected through the layer.
Type: Application
Filed: Nov 16, 2011
Publication Date: Jun 7, 2012
Patent Grant number: 9316593
Inventors: Michael Switkes (Somerville, MA), Mordechai Rothschild (Newton, MA)
Application Number: 13/297,657
International Classification: G01N 21/55 (20060101); G01J 4/00 (20060101);